In the field of audio engineering, digital technology has been used most often in the design of professional equipment. Recently, consumer video cassette tape recorders have incorporated digital technology and movement toward using digital technology in consumer audio equipment appears to be accelerating.
A major reason for this trend is that the PCM recording and playback system, which is made possible by combining a video tape recorder (VTR) with digital technology, has a much broader dynamic range than do conventional analog tape recorders. Another reason is that in comparison with those conventional recorders, the PCM system has practically no wow and flutter. Also, the PCM systems' frequency and distortion characteristics are substantially superior to those of analog systems.
A PCM audio system connected to a VTR requires a digital signal processor to transform the PCM signal format to and from the appropriate television signal format. The format for the PCM audio signal may be the one prescribed by the EIAJ (Electronic Industries Association of Japan) Technical File: STC-007, which employs bit error correction schemes together with interleaving techniques. This format will be described in detail below.
Encoded PCM audio signals in a TV signal format contain various control signals as well as the PCM audio signals. The control signals are used to control the PCM decoders, as will be explained below.
Conventional PCM signal processors for decoding encoded PCM signals do not adequately detect and correct errors in the control signals. One reason for this inadequacy is that conventional signal processors use the same techniques to correct control signals as to correct audio signals, and those techniques do not work well for control signals.